There exists a need in a vast number of industrial applications to connect or otherwise couple tubing, piping and fixtures, in such a way that leaks are prevented. While leak prevention is always desirable, it is an absolute necessity in applications where dangerous substances, e.g., caustic agents, explosive agents, flammable agents, toxic and/or biological agents, are being handled due to personal health and safety concerns, process efficiency concerns, and to prevent damage to property adjacent to potential leaks.
In many industrial applications, for instance in pharmaceutical and chemical research facilities, chemical and pharmaceutical processing plants, semiconductor manufacturing facilities and other similar facilities, corrosive materials are necessarily and routinely handled and disposed of. Corrosive materials present special handling and disposal problems in that traditional piping systems, which include steel, iron, copper and various plastic pipes, connectors and fixtures, are incapable of handling many corrosives due to the chemical reactivity or solubility of these materials. Corrosive materials, including strong acids, strong bases, and strong solvents would, sooner or later, “eat through” or otherwise destroy these materials, resulting in their failure.
In industry, the problem of corrosive materials is often dealt with by employing glass or ceramic (hereafter “glass”) pipes and tubes (hereafter “pipes”). Such materials have the advantage of not being reactive towards most chemical agents, with the additional advantage of being resistant to temperature extremes. Thus, many industrial applications in which corrosive agents are handled today employ, at least in part, glass piping.
Despite its advantages, glass piping also has certain critical disadvantages. Most notably, glass piping is extremely brittle. Glass piping is also very inflexible. Stress applied to glass tubing during the course of installation (due to dropping, overtightening of coupling devices, deflections from “straight” connections between glass components and other stresses occasioned by both proper and improper installations) or in the course of use, often leads to cracks, fractures and breaks. Such breaks are often difficult to repair due to the rigidity and fragility of glass pipe sections adjoining the broken section. These disadvantages make the installation, maintenance and use of glass piping systems difficult and expensive. These disadvantages also lead to environmental and workplace hazards which are considered undesirable by regulatory agencies such as the EPA and OSHA.
Piping systems comprising non-glass, non-reactive materials such as PTFE (polytetrafluoroethylene, often referred to—along with FEP and PFA—by DuPont's trade name Teflon®) have been proven to be an effective substitute for glass piping. Like glass piping, Teflon piping (typically, but not necessarily made from extruded or compression molded PTFE) is non-reactive with almost all chemical agents. Unlike glass piping, however, Teflon piping is not brittle and is not inflexible.
However, certain Teflon piping systems currently used in industry also have certain disadvantages for large system applications. In some Teflon piping systems, pipes are connected via threading. In practice, such Teflon piping is supplied in long unthreaded sections which are then cut to the needs of a particular application. After being cut, the installer must impart threading onto the pipe. Threading on the pipe sections is accomplished “in the field”, i.e., by the installation contractor, and not by the pipe or fixture manufacturer. Such field threading is technically difficult and is often performed improperly, leading either to wasted pipe (if the improper threading is detected) or worse, less than adequate sealing between sections (if the improper threading is not detected). The threaded joints can also be difficult to join properly with their potential for cross-threading, or over or under tightening.
Threaded Teflon piping sections are also difficult to replace or repair because threaded pipes are not easily disassembled. In any sequential series of connected threaded pipes, removing a “middle” pipe section could require sequentially disassembling all or most pipe sections from one end of the series. This is because pipe sections cannot individually be unthreaded (unscrewed) from neighboring sections without necessitating disassembly of other sections “down the line” and/or “up the line”. This problem, while always troublesome due to cost and time expenditures, is particularly vexing in long piping systems having many sequential joints.
Further, threaded Teflon pipes of a given inner diameter must be made with relatively thick sidewalls to accommodate the threading process, which necessarily removes sidewall material. The result is that thicker, heavier and thus more expensive piping must be employed. Put another way, thinner, less expensive piping may often be adequate but for the need for excess thickness at the ends of the tubings to accommodate a threaded connection.
Other forms of Teflon tubing systems joined by other methods are also available such as: small diameter systems joined by flare- or compression fittings, butt welded tubing systems, or tubing systems with sanitary end connections. These systems are generally not found not suitable for the applications in which threaded systems, have historically been used because they are often too small, and/or require complex and difficult to use field welding equipment, and/or are much more expensive, and/or are very thin-walled, allowing too much permeation, and/or are not sufficiently rigid to permit installation of systems that employ gravity draining.
In addition to straight section piping, almost all laboratory chemical disposal systems employ a plumbing fixture known as a trap, e.g., P-traps (the “P” deriving from the shape of the fixture). The P-trap is typically attached at its vertical end to the drain outlet of a sink, and at its horizontal end to a plumbing system. Even where the P-trap of the piping system is Teflon, the sink is often glass, or other rigid material.
There is often difficulty connecting the Teflon piping or a P-trap to a glass sink. In connecting Teflon piping or a P-trap to a glass sink, known coupling devices comprising Teflon, such as the Schott Process Systems, Inc.'s No. 6611 B/P Drainline Coupling, have been used, in which a glass-to-Teflon and Teflon-to-Teflon primary seals are formed, but in which there is no Teflon secondary seal. The coupler is held in place on the glass and on the Teflon pipe via friction resulting from rubber ribbing, grooves or other rubber portion in effect forming secondary rubber seals. The resulting seal, being rubber, is not impervious to corrosive agents which, when in contact with rubber, cause it to eventually corrode. Moreover, excess tightening of a coupling device to ensure the primary seal holds is of very little value, since the brittleness of the glass limits the possible degree of tightening. Often a faulty glass-to-Teflon seal is masked by the rubber secondary seal. After installation, the rubber seal becomes corrupted and fails. Thus, there is no glass-to-Teflon coupling device in which effective primary and secondary seals are capable of being formed.
Moreover, the P-trap is typically formed with beading at either end. Although beading geometry helps in forming a primary seal between the walls of the coupling device, it also significantly hinders the formation of a secondary seal. The larger diameter of the bead makes the presence of additional ribs “behind” where the bead is to be inserted difficult (since the bead must be forced past any such ribs to be seated within the coupler).
Finally, it is the nature of Teflon, and thus Teflon piping, to deform elastically and plastically. Plastic deformation or “creep” may cause difficulties in coupling Teflon pipes both to glass and to other Teflon piping. Tightening a coupling device often works well initially but requires retightening to account for creep caused by the original tightening. Creep lessens and ceases to be a practical problem after initial plastic deformation has taken place. In glass-to-Teflon connections the problem noted above with respect to an inability to overtighten due to glass brittleness is exacerbated by plastic deformation.